Extending the optical spectrum of an optical network

ABSTRACT

Systems and methods include, for operation on an optical fiber in an optical network with the optical fiber having extended optical spectrum that include a plurality of bands including at least the C-band and one or more additional bands, segmenting the plurality of bands by distance based on different transmission specifications for the plurality of bands based on fiber types and amplifiers used for corresponding bands; and placing one or more channels on the optical fiber in a corresponding band of the plurality of bands based on a distance between nodes associated with each of the one or more channels. The segmenting is based on a metric that is a function of fiber type of the optical fiber and amplifier performance for amplifiers used in the plurality of bands.

CROSS-REFERENCE

The present disclosure is a continuation-in-part of U.S. patent application Ser. No. 17/082,218, filed Oct. 28, 2020, which is now U.S. Pat. No. 11,196,504, with an issue date of Dec. 7, 2021, the contents of which are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to optical networking systems and methods. More particularly, the present disclosure relates to systems and methods that allow network nodes of an optical network to operate within an extended spectral band of optical signals.

BACKGROUND

Generally, the fiber-optic communication industry is facing a capacity crunch, driven by relentless bandwidth growth. Recent reports indicate that growth rates ranging from about 26% to about 37% are expected. Much of this traffic growth is expected between users and data centers and between one data center and another.

Given these network bandwidth growth trends, the fiber-optic communication industry is focused on coming up with Capital Expenditures (CapEx) and Operating Expenditure (OpEx) efficient solutions. For example, there seems to be at least five hardware-centric options, each with their own associated tradeoffs, being pursued by the industry.

A first option for handling the increased growth in optical networks includes converting fixed-grid optical line systems to flexible grid systems, which has been a fast and simple way to obtain a short-term boost (e.g., about 20%) in capacity via improved spectral utilization. However, this expansion option has essentially been exhausted in commercial equipment, and network deployments of this equipment are proceeding apace.

A second option includes employing parallel optical line systems via either separate fiber strands or multi-core fiber Spatial Division Multiplexing (SDM). This option provides additional resilience against fiber or line system component failures.

A third option includes increasing the channel spectral efficiency using higher order modulation constellations. However, this option has diminishing returns since the addition of each two extra bits (i.e., a linear increase) results in about 3.5 dB decrease in reach performance (i.e., an exponential decrease).

A fourth option includes considering network infrastructures that might increase the Signal-to-Noise Ratio (SNR) or Optical SNR (OSNR). For example, some research is directed to the use of Ultra-Low-Loss (ULL) fibers. Given a fixed amplifier spacing and complete fiber replacement, a difference between conventional Single-Mode optical Fiber (SMF) (i.e., about 0.2 dB/km) and a ULL fiber (i.e., about 0.1424 dB/km) is about 4.6 dB, which produces about a 3 dB gain in SNR. Unfortunately, though, expected capacity gain (e.g., about 20%) is a one-time benefit, sufficient for about six months' worth of traffic growth.

A fifth option includes accessing an expanded fiber spectrum from C-band (i.e., 1530 nm to 1565 nm) to an extended C-band to include L-band (i.e., 1565 nm to 1625 nm). This option affords a more significant capacity increase of over 100% with a modest increase in line system cost and propagation penalty. Since this option appears to provide better results, the industry has moved toward solutions that operate within an extended band, particularly the amplification of optical signals within this extended band that are transported throughout an optical network.

However, the current state of extended band amplification systems (e.g., utilizing extended C-band and/or extended L-band) suffers from a lack of infrastructure in the field. Thus, to implement these extended band solutions, potentially expensive developments would be needed. Also, other issues have arisen with respect to the incorporation of this technology in optical networks.

Presently, companies providing optical services have indicated that they are reluctant to invest in the development of certain modules (e.g., Wavelength Selective Switching (WSS) components, Optical Channel Monitoring (OCM) components, contentionless WSS (CWSS) components, tunable filters, etc.) that could cover the extended spectral range. Although amplifiers may be relatively easy to design and build, there would normally be a delay in the availability of other modules (e.g., WSS components, etc.). It appears that there are currently no programs that have kicked off in this regard to incorporate this needed infrastructure to operate within the extended band.

Therefore, cost is usually restrictive in the development of extended band systems. Lower volumes (at least initially) will result in premium costs up front. Amplifier costs would increase due to extra power required to support the additional spectrum and to overcome the Gain Flattening Filter (GFF) losses. Also, Raman amplification would require an extra pump to avoid compromising gain and ripple. Therefore, there is a need in the field of optical communication networks to provide systems for handling the ever-increasing demand and to provide systems that can be implemented in a cost-effective way.

BRIEF SUMMARY

The present disclosure pertains to various systems and methods for extending the spectrum of optical channels. The C-band spectrum includes a band of wavelengths ranging from about 1530 nm to about 1565 nm and is commonly used for the transmission of optical signals. Some systems are being developed that not only operate in the C-band but are also configured for operating in the L-band, which includes an additional band of wavelengths ranging from about 1565 nm to about 1625 nm. However, the C+L band systems typically require separate transmission equipment for each of the separate bands. Therefore, the present disclosure provides systems in which the same equipment can be used for an “extended” band, whereby the extended band includes the C-band wavelength channels plus additional channels less than the entire L-band, as well as to shorter wavelengths in the S-band but not including the entire S-band. In this respect, the new spectrum described herein may be referred to as an “extended C-band.” The extended C-band may push the bandwidths beyond just the C-band wavelengths to include wavelengths higher than the C-band (within part of the L-band) and wavelengths lower than the C-band (within part of the S-band). In some implementations, the spectrum may be expanded to includes wavelengths from about 1524 nm to about 1577 nm.

According to one implementation of the present disclosure, a method includes the step of establishing an extended optical spectrum having a plurality of optical channels for transmission of optical signals within an optical network. The extended optical spectrum may include at least the C-band plus one or more sub-bands, the C-band having a range of wavelengths from about 1530 nm to about 1565 nm. Each of the one or more sub-bands may have a range of wavelengths including at least one optical channel outside the range of the C-band. The method further includes the step of segmenting the extended optical spectrum into a local band and an express band having different transmission specifications. The local band may be configured for transmission of optical signals between nodes having a relatively shorter distance therebetween. The express band may be configured for transmission of optical signals between nodes having a relatively longer distance therebetween. The combination of the one or more sub-bands covers less than the L-band having a range of wavelengths from about 1565 nm to about 1625 nm and/or less than the S-band having a range of wavelengths from about 1460 nm to about 1530 nm.

According to another implementation of the present disclosure, a tunable edge filter may be configured to establish an extended optical spectrum having a plurality of optical channels for transmission of optical signals within an optical network. The extended optical spectrum may include at least the C-band plus one or more sub-bands, where the C-band has a range of wavelengths from about 1530 nm to about 1565 nm. Each of the one or more sub-bands may have a range of wavelengths including at least one optical channel outside the range of the C-band. The tunable edge filter may be further configured to segment the extended optical spectrum into a local band and an express band having different transmission specifications. The local band may be configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, and the express band may be configured for transmission of optical signals between nodes having a relatively longer distance therebetween. The combination of the one or more sub-bands may cover less than the L-band having a range of wavelengths from about 1565 nm to about 1625 nm and/or less than the S-band having a range of wavelengths from about 1460 nm to about 1530 nm.

According to yet another implementation of the present disclosure, a node operating in an optical network in provided. The node may include an add/drop device configured to add and drop optical channels within an extended optical spectrum having a plurality of optical channels for transmission of optical signals within the optical network. The extended optical spectrum may include at least the C-band plus one or more sub-bands, wherein the C-band has a range of wavelengths from about 1530 nm to about 1565 nm. Each of the one or more sub-bands may have a range of wavelengths including at least one optical channel outside the range of the C-band. The node further includes a filter for segmenting the extended optical spectrum into a local band and an express band having different transmission specifications, wherein the local band may be configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, and the express band may be configured for transmission of optical signals between nodes having a relatively longer distance therebetween. The combination of the one or more sub-bands may be configured to cover less than the L-band having a range of wavelengths from about 1565 nm to about 1625 nm and/or less than the S-band having a range of wavelengths from about 1460 nm to about 1530 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein with reference to the various drawings. Like reference numbers are used to denote like components/steps, as appropriate. Unless otherwise noted, components depicted in the drawings are not necessarily drawn to scale.

FIG. 1A is a diagram illustrating a first extended optical spectrum having multiple segments of optical sub-bands, according to various embodiments of the present disclosure.

FIG. 1B is a diagram illustrating a second extended optical spectrum having multiple segments of optical sub-bands, according to various embodiments of the present disclosure.

FIG. 2 is a diagram illustrating a portion of an optical network where a first network node transports optical signals consuming channels in both a local band and an express band of an extended optical spectrum to a second network node, according to various embodiments of the present disclosure.

FIG. 3 is a diagram illustrating the portion of the optical network of FIG. 2 from a perspective of the entire extended optical spectrum, according to various embodiments of the present disclosure.

FIG. 4 is a diagram illustrating a segmented band transmission system, according to various embodiments.

FIG. 5 is a flow diagram illustrating a process for creating an extended optical spectrum, according to various embodiments.

FIG. 6 is a diagram illustrating a third extended optical spectrum having multiple optical sub-bands, according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for extending or expanding the spectral band for transporting optical signals within an optical communication system. There has been a push in the optical networking industry towards creating an extended band to increase the number of optical channels. Also, one focus of the present disclosure is to extend the optical spectrum for amplified transport systems.

Research in the field of extended band amplification has led to various systems using similar extended band concepts. Some solutions have included Raman-based extended bandwidth amplification line systems. Current Reconfigurable Optical Add/Drop Multiplexing (ROADM) components and Wavelength Selective Switching (WSS) components are traditionally designed to only operate inside the conventional C-band (i.e., a wavelength range from about 1530 nm to about 1565 nm). Since these components are generally designed only for this range, extension of the operational band would be expensive and may still take years to implement. Also, rare earth doped fiber amplifiers (e.g., Erbium-Doped Fiber Amplifiers (EDFAs)) normally have Gain Flattening Filters (GFFs) which are much more difficult to produce if the bandwidth coverage is extended. The extended band also negatively impacts the amplifier Noise Figure (NF) and gain ripple performance, and drives up the pump power requirements, thus making the EDFA less efficient.

In addition, extended band WSS components are possible to manufacture, but there is a balance between the number of pixels in the switching elements, the band of operation, and the effective filtering resolution which drives up WSS cost as the bandwidth increases. Also, as a result, the performance of the device may typically decrease. Modem micro-amplifiers may have different NFs across extended bandwidth. Micro-amplifiers may be single channel amplifiers and may be configured to cover only a portion of the system spectrum occupied by the modem. In some implementations, the micro-amplifiers do not need spectral flattening. Raman amplification may require extra pumps and may start having issues with overlap of Raman pump and data signal wavelengths.

Regarding performance and capacity, most system vendors today have implemented modems that operate across about 4.8 THz of the C-band spectrum (e.g., about 191.2 THz to about 196.0 THz). Going from about 4.8 THz to about 6.0 THz would be a 25% increase in available spectrum. Amplifier Noise Figures (NFs) and gain ripple would increase appreciably due to the number and depth of the GFFs. Modem micro-amps would also suffer from some amount of NF penalty. Even with additional GFFs, the ripple would be larger than existing amplifiers, which results in an Optical Signal-to-Noise Ratio (OSNR) penalty. Also, WSS bandwidth would degrade proportionally with the spectral range increase due to Liquid Crystal on Silicon (LCoS) resolution, although this issue could be addressed with next generation LCoS technology, which may still be years away.

One solution for extending the optical band can be found in a related patent (U.S. Pat. No. 8,280,258) having at least one common inventor, the disclosure of which is incorporated by reference herein. This issued patent anticipated the use of an extended band, where the optical spectrum can by partitioned into “express” and “local” components, where local transmission includes sending optical signals to an adjacent node located a relatively shorter distance away, while express transmission includes sending optical signals to an adjacent node located a relatively longer distance away. Some embodiments may be configured to place Optical Phase Conjugation into the “express” path to manage long-reach nonlinear effects. The present disclosure continues these concepts and includes further developments in this field, such as, for example, a one-band system and an overlapping sub-band system, as described below.

By providing an extended spectrum and splitting the spectrum into “express” and “local” band, the express paths can be used herein to avoid the limitations outlined above with respect to conventional systems. In the present disclosure, ROADMs and associated components can be used only in the local path and over the currently defined C-band spectrum. Optimal optical power density is somewhat independent of reach (i.e., about the same in both paths). Optimal optical power density is also somewhat independent of the modulation format, although achievable reach may be sensitive to constellation cardinality.

In an example, an optical network is an optical communication system serving various locations across a geography, e.g., North America. It may be noted that smaller networks (e.g., European optical networks) may provide more opportunities for implementing the extended band systems and methods described in the present disclosure, particularly for separating express and local channels. However, even continental-sized North American networks may provide sufficient opportunity for implementing a reasonable separation between express and local connections. Additionally, such network configuration could be a good fit for global cloud networks, which may need high-capacity “express” connections between centralized data center locations.

The optical network includes a plurality of nodes and in a nationwide network (U.S.), the major inter-node distances may be about 500 to 1000 km. The distance across North America is about 4000 km. The optical network would intuitively benefit from long optical reach and transparency.

The major driver for extended band operation is the efficient use of the transmission fiber asset. Since spectral efficiency gains are slowing as the transponder encoding and decoding technologies approach the Shannon Limit, the capacity per fiber is not expected to increase significantly without an increase in the useable transmission bandwidth. One option for extended band in the transmission fiber is the use of all-Raman amplification. A limitation of an all-Raman extended band system, however, is the ability to provide bulk gain elements for ROADM components, add/drop components, and transponders/modems/transceivers. As noted above, designing EDFAs with the same bandwidth as an all-Raman transmission portion would be expensive and complex and may result in inferior noise performance.

Nevertheless, the present disclosure is directed to advancing the extended band concept by introducing various novel features. The systems and methods described in the present disclosure may include embodiments that can be grouped into two categories based on the approach taken to segregate the band. A first category may be referred to as a “one-band system” and the second category may be referred to as an “overlapping sub-band system.”

One-Band System

The “one-band system” may include a setup where EDFAs and/or Raman amplifiers cover a continuous spectrum. The EDFAs and Raman amplifiers do not need to cover the same spectrum, as indicated below regarding an express gain ripple being outside of a ROADM window that can be equalized by a separate Dynamic Gain Equalization (DGE) module.

In the one-band system, a tunable filter (e.g., an edge filter or fixed filter) can be used to split the overall spectrum into express and local bands. The local band may serve shorter connections with fewer spans and may include less expensive (lower performing) amplifiers, such as Semiconductor Optical Amplifiers (SOAs).

Also, the express band, in some embodiments, may be further split into “normal-express” and “ultra-express” sub-bands. A Gain Flattening Filter (GFF) may be used to provide tighter flatness specifications in the express band. The flatness characteristics may have looser specifications in the local bands. This may result in a simplified GFF design, reduced costs, and reduced insertion loss, thereby improving Noise Figure (NF) especially in the express portion of the band.

In some preferred embodiments, the express channels may be placed in longer wavelengths if the stimulated Raman pumping is beneficial, as induced by co-propagating “local” channels. When external Raman pumps are used, the pump wavelengths may be arranged to provide gain to express channels, thereby minimizing overall system cost and power. Although gain tilt in the transition regions may be a problem, this may be mitigated by ROADM channel power control. Also, express gain ripple may be outside of a ROADM window, equalized by a separate DGE module.

Thus, the one-band system can include different components across different portions of the one band. Also, local and express (as well as normal-express and ultra-express) traffic can be segmented in different portions on the one band, as described herein.

Overlapping Sub-Band System

The overlapping sub-band system may be split into two functional segments: a) extended-band transmission and b) photonic functions (e.g., ROADM, add/drop, and transponder functions), where the photonic functions require bulk amplification. The photonic functions may be separated into sub-bands where each sub-band is a portion of the full band. In some cases, each sub-band may overlap in frequency (wavelength) with at least one other sub-band. The purpose for this overlap may be to allow for the design of bulk amplifiers (e.g., EDFAs), which provide high performance and high efficiency in each sub-band of interest. It may be difficult to create an EDFA with a gain region which drops sharply at the edges of the band. By allowing the sub-bands to overlap, this restriction is essentially eliminated. When channels from different spectral sub-bands are split and then recombined, the spectrum can be filtered to prevent Multi-Path Interference (MPI) or cross-talk from other sub-bands. While the sub-bands are spatially separated into parallel sub-band paths inside “photonic functions,” the spectrum, in some cases, may not need to be sharply truncated. However, such truncation can be performed when the spatial paths are recombined, i.e., via tunable filters, as described below.

In the overlapping sub-band system, the WSS technology may follow the same or similar design paradigm. The cost tradeoff of multiple WSS modules vs. a single wideband module is not as strong as the EDFA modules, but this is expected to be offset at the system level by allowing the system to selectively deploy only the WSS modules needed for the processed sub-bands at a given site.

The transponders/modems/transceivers in the overlapping sub-band system can also be designed in sub-bands thereby simplifying the micro-EDFA design and retaining the noise performance within those bands.

The overlap in the gain ranges of the sub-bands does require filtering at the system boundary between sub-band photonics and the extended band transmission to prevent crosstalk and multipath interference. This is achieved through a combination of the WSS modules in combination with two or three port optical filters.

Operating Principles

FIG. 1A shows a representation of a first extended optical spectrum 20A for the transmission of optical signals. The optical spectrum 20A may be viewed as being “extended” in the sense that it extends beyond the normal C-band (e.g., about 1530 nm to about 1565 nm) range. According to various embodiments of the present disclosure, the extended optical spectrum 20A may then be partitioned into certain sub-bands. For example, the extended optical spectrum 20A may include a “local” sub-band 22 and an “express” sub-band 24. The local sub-band 22 may include a conventional ROADM passband, which may include up to 88 optical channels divided into 50 GHz bands and may be similar to or the same as the frequency range of the C-band (e.g., about 191.2 THz to about 196.0 THz). Also, the local sub-band 22 may include ROADM-based collector and grooming. In some embodiments, the express sub-band 24 may include up to about 40 channels divided into 50 GHz bands. The express sub-band 24 may be band-based and may be ungroomed.

The express sub-band 24 may be separated from the local sub-band 22 by using a tunable passband filter. In some embodiments, the tunable passband filter may be configured to further divide the express sub-band 24 into multiple additional sub-bands, as depicted in FIG. 1B. For example, from the channels of the express sub-band 24, the tunable passband filter may divide the express sub-band 24 at least into a “normal-express” sub-band 24A and an “ultra-express” sub-band 24B. According to some embodiments, the ultra-express sub-band 24B may include wavelengths that are separated from the local sub-band 22 by the normal-express wavelengths.

Thus, the embodiments of the present disclosure may use a tunable filter (e.g., an edge filter) to separate the local sub-band 22 from the express sub-band 24 (or express sub-bands 24A, 24B). The filtering may occur at express nodes in the network, which may include those nodes that are more greatly separated from other nodes in the network. Also, express channels can be bypassed in local nodes. The tunable edge may be aligned at the edge of conventional C-band (e.g., at about 1565 nm). The edge may be defined by the ROADM boundary, but may also overlap with the conventional ROADM passband. In some embodiments, the edge may also be separated by a dead zone gap, although this may be considered in some cases to be a waste of spectrum.

According to another embodiment, the second extended optical spectrum 20B of FIG. 1B shows the local sub-band 22 and the express sub-bands 24A, 24B. Also, the extended optical spectrum 20B may include a lower sub-band 26 having wavelengths lower than the local sub-band 22 including channels of the C-band. In this respect, the wavelengths of the extended optical spectrum 20B may extend from both ends of the C-band, where the lower sub-band 26 includes shorter wavelengths (and higher frequencies) than the C-band and the express sub-bands 24A, 24B include longer wavelengths (and lower frequencies) than the C-band.

According to the various embodiments of the present disclosure, a conventional C-band (i.e., about 1530 nm to 1565 nm) could be extended to an extended band (or super C-band). For example, the extended band may range from about 1524 nm to about 1577 nm. In this case, the lower sub-band 26 may include wavelengths ranging from about 1524 nm to 1530 nm. The local sub-band 22 may include wavelengths ranging from about 1530 nm to about 1565 nm. Also, the express sub-bands may include wavelengths ranging from about 1565 nm to about 1577 nm.

The extreme regions of this extended optical spectrum 20A, 20B, which may include one or more of sub-bands 22, 24, 24A, 24B, 26, may include operating specifications that may be higher than the specifications for the C-band range (e.g., the local sub-band 22). With higher specifications, these sub-bands may be used for allowing express traffic to flow under the higher specifications. For example, the amplification in sub-bands 24, 24A, 24B, 26 may have greater performance than amplification in the local sub-band 22.

The magnitude to which the extended band may be extended may be factor of the size of the network and how far apart the various nodes are positioned from each other. For example, if a large percentage of the network nodes are located far apart, thereby benefiting from communication along the express sub-bands 24A, 24B, then the extended band may be extended by a larger amount. However, if a low percentage of the network nodes are located far apart (e.g., such as in some European networks), then the extended band may be extended to a lesser amount since most traffic may be considered to be local traffic. Thus, the range of the entire extended spectrum may be modified as needed according to how many channels may be needed for express traffic (and how many channels may sufficiently be used for local traffic).

The better transmission specification may be given to the extremes of the extended optical spectrums 20A, 20B, which may include, for example, the express sub-bands 24, 24A, 24B and, in some embodiments, may further include the lower sub-band 26. For instance, the better transmission specifications may include lower loss in the fibers, better (lower) Noise Figures (NFs), etc. Also, Raman amplifiers may be configured to operate better in the extremes of the extended optical spectrums 20A, 20B. Also, the Stimulated Raman Scattering (SRS) losses may be based on a narrower spectrum and may be less in the extremes.

The local sub-band 22 may correspond to part or all of the C-band, which includes frequencies ranging from about 195.90 THz to about 191.55 THz, which may include 88 channels each spaced by 50 GHz. These frequencies corresponding to wavelengths ranging from about 1530 nm to about 1565 nm. The express sub-band 24 and/or express sub-bands 24A, 24B may include wavelengths ranging from about 1565 nm to about 1577 nm.

FIG. 2 is a diagram illustrating an embodiment of a portion 30 of an optical network where a first node 32 transports optical signals consuming channels over the entire extended spectrum (e.g., the first extended optical spectrum 20A, the second extended optical spectrum 20B, or other suitable extended range). Thus, transmission is made in both the local sub-band 22 (e.g., C-band) and any additional sub-bands (e.g., express sub-bands 24, 24A, 24B, lower sub-band 26, etc.) to a second node 34.

Optical signals are transported over a transmission fiber 36 having multiple spans, including the local sub-band 22 and express sub-band 24. The first node 32 includes a ROADM 38 that operates in a conventional manner for transmitting and receiving C-band spectrum signals with “local” nodes. For transporting optical signals over the transmission fiber 36, the first node 32 includes a tunable edge add component 40, an express channel multiplexer 42, and a post-amplifier 44. The signals are transmitted over the transmission fiber 36 and received by the second node 34. The second node 34 includes a pre-amplifier 46, a tunable edge drop component 48, an express channel demultiplexer 50, and a ROADM 52.

The tunable edge add component 40 and the tunable edge drop component 48 may be referred to as “tunable edge filters” and may be configured to tune the respective node for operation in one or more of the sub-bands described with respect to FIGS. 1A and 1B. Also, the tunable edge add component 40 and the tunable edge drop component 48 may include an add/drop device for adding and/or dropping channels based on the sub-bands to which the tunable edge filter is tuned when located at an express node. According to some embodiments, a network node may include both a filter (e.g., tunable edge filter) and an add/drop device for adjusting to the particular extended band in which the node is configured to operate. The tunable edge add component 40 and the tunable edge drop component 48 may include a bypass function such that express channels bypass ROADM components 38 and 52 when located at a local node.

It should be noted that FIG. 2 shows the transmission of signals in a single direction (i.e., from the first node 32 to the second node 34). However, it should be understood that communication may be bi-directional, where the second node 34 may transmit signals in the opposite direction over the transmission fiber 36 to the first node 32. In this respect, the first and second nodes 32, 34 may each include the components for receiving or transmitting, respectively, described with respect to the other node.

The ROADM 38 of the first node 32 provides add/drop functionality for “local” channel spectrum coverage. The tunable edge add component 40 of the first node 32 is configured to define the separation of the optical spectrum 20 into the two or more sub-bands (e.g., local sub-band 22 and express sub-band 24). The express channel multiplexer 42 may be a low-cost, static component implemented using Arrayed-Waveguide Grating (AWG) filters. Alternatively, the express channel multiplexer 42 can be a more complex WSS-based structure, but with WSS components required to cover only a limited spectrum range.

The second node 34 includes the tunable edge drop component 48 for removing the express channels and sending these express channel signals to the express channel demultiplexer 50 for processing. The local channels separated by the tunable edge drop component 48 are provided to the ROADM 52 for normal processing of the local channels.

In this embodiment, the first node 32 may use the same components across the entire extended spectrum 20A, 20B. However, according to the implementations described in the present disclosure, these components may be utilized in a way where the filtering procedure includes segmenting the spectrum into two or more sections having different specifications (e.g., Noise Factor (NF), gain ripple, etc.). Therefore, instead of attempting to maintain the same specifications for each partial spectrum, the components may be modified from conventional components to allow them to either operate over the entire extended band or to split them up to operate over one (or more) of the partial spectrums.

According to some embodiments, the channels (e.g., channels of the local sub-band 22) having higher specifications (e.g., less noise and gain ripple) may be allocated for regions of the network having a longer reach, which may include the additional channels (e.g., channels in sub-bands 24, 24A, 24B, 26) at the extremes of the extended band. Also, the local sub-band 22 may include channels that are allocated for shorter reach applications. For example, a longer reach application (e.g., Boston to Chicago) for connection between nodes that are located relatively farther apart may be configured to operate with the express sub-band 24, while a shorter reach application (e.g., Philadelphia to New York) for connection between nodes that are located relatively closer together may be configured to operate with the local sub-band 22. The lower sub-band 26 may be grouped with express sub-bands or the local sub-band 22 and thereby may be allocated as either express band or a local band.

The tunable edge add component 40 and tunable edge drop component 48 may be configured as WSS components for add/drop functions with the added functional characteristic of enabling a tunable filtering process to split the continuous extended band into sub-bands for operation within one or more of the sub-bands. The express channels (e.g., sub-bands 24, 24A, 24B, 26) can be added by the express channel multiplexer 42 and dropped by the express channel demultiplexer 50. The filters of the tunable edge add component 40 and tunable edge drop component 48 may be configured to split the continuous spectrum or split one of the sub-bands (e.g., express sub-band 24).

FIG. 3 is a diagram showing the portion 30 of the optical network shown in FIG. 2 from a perspective of the entire optical spectrum as extended with respect to the various embodiments of the present disclosure. As shown in FIG. 3 , the portion 30 may include bi-directional communication between a first express node 62 and a second express node 64. Communication between adjacent pairs of nodes 62A, 62B, 62C, 62D may include an extended spectrum 66, which includes a local band 68 and an express band 70. Handling of local channels in the local band 68 can be performed separately from the handling of express channels in the express band 70.

Each node 62A, 62B, 62C, 62D is capable of processing both local channels and express channels. In this example, the first (express) node 62A includes an add/drop component 72 for multiplexing and demultiplexing channels in both the local band 68 and the express band 70. A local add/drop component 74 of the second (local) node 62B is configured for multiplexing and demultiplexing channels in just the local band 68. Similarly, the third (local)node 62C includes a local add/drop component 76 for multiplexing and demultiplexing channels in just the local band 68. The fourth (express) node 62D includes an add/drop component 78 for multiplexing and demultiplexing channels in both the local band 68 and the express band 70. The add/drop components 72, 74, 76, 78 connect the corresponding ROADM components 80A, 80B, 80C, 80D in the local band 68 and the Thin Optical Add/Drop Multiplexing (TOADM) components 92A, 92D in the express band 70 and also connect to corresponding transceivers 82, 84, 86, 88, respectively.

In an example where nodes 62A and 62D are considered to be “express” nodes and nodes 62B and 62C are considered to be “local” nodes, the express nodes 62A, 62D use the TOADM components 92A, 92D for add/drop while the local nodes 62B, 62C use the TOADM components 92B, 92C for bypass of the express channels. The express channels will bypass the ROADM components 80B, 80C at the local nodes 62B, 62C, but will be added/dropped by the ROADM components 80A, 80D at the express nodes 62A, 62D.

The overall system of the portion 30 of the optical network includes a Dynamic Gain Equalizer (DGE) element 100, which covers exclusively the express band 70, as shown in FIG. 3 . Spectrum equalization on the local band 68 may be accomplished conventionally through the ROADM components 80.

In some embodiments, the express add/drop components 72, 78 may be configured as WSS components for operations with the ROADM components 80 and/or TOADMs 92. The express add/drop components 72, 78, according to various embodiments, may include reflective ports that are not controlled. The reflective ports may have flat reflective surfaces that are configured to reflect to a single port. Thus, the channels outside of the normal control pixels for the components 72, 78 may fully reflect off the reflective surfaces to the single port. This reflective characteristic may be applied to other bands or sub-band regions by causing outside channels to reflect to one port. For example, the unused channels may be reflected to the express band. The rest of the channels (e.g., in-band channels) may be pixelized by the corresponding ROADM component 80.

FIG. 4 is a diagram illustrating an embodiment of a segmented band transmission system 110 for transmission of extended band optical signals between a first express node 112 and a second express node 114. The first express node 112 includes a full-band amplifier device 116 configured for amplifying the entire extended band (e.g., optical spectrum 20A, 20B) from output ports of the first express node 112. The optical signals amplified by the full-band amplifier device 116, associated with the first express node 112, are transmitted to a full-band amplifier device 118 associated with the second express node 114. In the opposite direction, optical signals from the second express node 114 are amplified by post-amplifier elements of the full-band amplifier device 118 and transmitted to the first express node 112 having pre-amplifier elements of the full-band amplifier device 116. Also, intermediate nodes or line amplifiers are positioned between the nodes 112, 114 and may include one or more full-band amplifiers. In FIG. 4 , two intermediate full-band amplifier devices 120, 122 are shown.

The full-band amplifier devices 116, 118, 120, 122 are configured as bi-directional devices and are configured to amplify the optical signals covering the entire extended spectrum (e.g., 20A, 20B), which may include the C-band plus additional wavelengths. The express nodes (e.g., second express node 114) may further include a sub-band amplifier 124 having filtering for processing of local and/or express signals. The filters of the sub-band amplifier 124 may be connected to sub-band components 126 (e.g., amplifiers, WSS components, etc.) for handling local channels of the optical spectrum.

The sub-band components 126 (e.g., amplifiers, WSSs, etc.) may be implemented with Rare-Earth Doped Fiber Amplifiers (REDFAs), SOAs, and/or Raman amplifiers. For sub-band applications, the REDFAs may be configured as micro-REDFAs that maintain noise performance with the respective sub-band. However, in the “one-band” application, the components may be configured to extend across the whole band, where the performance of the band is segregated with different specifications. Some components may be configured for full-band transmissions, while others may be configured to transmit over only a portion (e.g., one or more the sub-bands 22, 24, 24A, 24B, 26) of the entire spectrum. It should also be recognized that the components may be configured to operate in sub-bands that overlap with other sub-bands and/or may operate such that the components themselves have overlapping ranges that overlap at any points along the entire spectrum.

The embodiments of the present disclosure may include certain advantages over conventional system. For example, it may be noted that the present disclosure provides an option for Service Providers (SPs). For a small network (e.g., a European network), the present disclosure offers an option to separate express and local channels from each other for processing in two different ways. However, even continental-sized networks (e.g., a North American network) may provide sufficient opportunity for implementing a reasonable separation between local and express connections.

Also, the embodiments of the present disclosure may also be utilized by Global Cloud Providers. As such, the disclosed network configuration may be a good fit for Global Cloud Network companies, which may need high-capacity express connections between centralized data center locations.

When extending these optical wavelength bands, there may inherently be a range of performance across the spectrum that necessitates a need to differentiate traffic to particular bands based on performance. The present disclosure targets practical system-level design considerations (not lab-type concepts) with cost and complexity being some of the important parameters to consider in the creation of the extended spectrum.

FIG. 5 is a flow diagram illustrating an embodiment of a process 130 for creating an extended optical spectrum for use in an optical network. In this embodiment, the process 130 may include the step of establishing an extended optical spectrum having a plurality of optical channels for transmission of optical signals within an optical network, as indicated in block 132. The extended optical spectrum may include at least the C-band plus one or more sub-bands, where the C-band has a range of wavelengths from about 1530 nm to about 1565 nm. Each of the one or more sub-bands may have a range of wavelengths including at least one optical channel outside the range of the C-band. The process 130 may further include the step of segmenting the extended optical spectrum into a local band and an express band having different transmission specifications. The local band may be configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, and the express band may be configured for transmission of optical signals between nodes having a relatively longer distance therebetween. In some embodiments, a combination of the one or more sub-bands may cover less than the L-band, which has a range of wavelengths from about 1565 nm to about 1625 nm.

According to additional embodiments, the process 130 may be further defined, whereby the combination of the one or more sub-bands may cover less than half of the L-band. The one or more sub-bands may include a lower sub-band having a wavelength range with wavelengths less than the C-band, whereby the wavelength range of the lower sub-band may be less than half the range of wavelengths of the C-band. The step of establishing the extended optical spectrum may include establishing a range of wavelengths from about 1524 nm to about 1577 nm.

The process 130 may also be defined such that the specifications include one or more of Noise Factor (NF) and gain ripple. The transmission specifications of the express band may enable the optical signals transmitted by way of the express band to have a longer reach than the local band. The step of segmenting the extended optical spectrum may include segmenting bands that overlap.

The process 130 may further comprise the step of segmenting the express band into a normal express band and an ultra-express band, wherein the ultra-express band enables a longer reach than the normal express band. Also, the process 130 may further include the step of modifying the operating parameters of a plurality of optical components of a network node to enable the network node to operate over the extended optical spectrum. The process 130 may also include the step of enabling one or more of the optical components to operate over the entire extended optical spectrum and the step of enabling one or more others of the optical components to operate over one of the express bands and the local band.

FIG. 6 is a diagram illustrating a third extended optical spectrum having multiple optical sub-bands, according to various embodiments of the present disclosure. In particular, compared to FIGS. 1A-1B, FIG. 6 illustrates the complete optical fiber transparency window, along with corresponding amplifier types for each sub-band. Of note, the various approaches for segmenting optical spectrum into local, express, ultra-express, etc. bands are contemplated with the extended optical spectrum, i.e., the complete optical fiber transparency window.

The complete optical fiber transparency window is as follows (note, the wavelength values are approximate):

O-band 1260-1360 nm E-band 1360-1460 nm S-band 1460-1530 nm C-band 1530-1565 nm L-band 1565-1625 nm U-band 1625-1675 nm

The E-band includes the so-called water peak with respect to optical loss in the complete optical fiber transparency window. The C-band includes the lowest attenuation and is the original and mostly used band in DWDM deployments. The L-band has the next lowest attenuation and is being used as an expanded DWDM band.

From an amplification perspective, there are various amplification approaches known in the art and they can be classified as rare earth doped fiber, fiber Raman, and semiconductor. Types of rare earth doped fiber amplifiers include silica-based EDFAs, fluoride-based EDFAs, tellurite-based EDFAs, fluoride-based thulium-doped fiber amplifiers (TDFAs), fluoride-based praseodymium-doped fiber amplifiers (PDFAs), P-doped silica bismuth-doped fiber amplifier (BDFA), low-Ge silica BDFA, high-Ge silica BDFA, etc. Types of fiber Raman amplifiers include silica and tellurite-based amplifiers with different numbers of laser diodes (LD). Types of semiconductor amplifiers include linear optical amplifiers (LOAs), quantum-well semiconductor optical amplifiers (SOAs), and quantum-dot SOAs. Of course, the present disclosure contemplates emerging optical amplifier technologies. Also, of note, it is possible to construct an amplified to cover the entire transmission region (e.g., 1270-1670 nm) using a combination of BDFAs and EDFAs; of course, any subset is also contemplated.

The present disclosure contemplates using a plurality of the entire bands, O-band, E-band, S-band, C-band, L-band, and U-band, as well as a sub-bands of the full bands or sub-bands across adjacent bands, in a segmented manner based on the reach of traffic, i.e., local, express, ultra-express, etc. The segmented manner is based in part on the performance of the specific spectrum (e.g., from a loss perspective) and the performance of the optical amplifiers in the specific spectrum. For example, if a band's amplifier has a naturally worse noise performance, or ripple performance, there is a worsening of the Spectral Efficiency*Reach product. This lends itself to treating each band or sub-band differently, reserving the longest reach for the best product. That is, the local, express, and ultra-express designations can be based on the Spectral Efficiency*Reach product for each band or sub-band.

Of note, the Spectral Efficiency*Reach product can be a function of the optical amplifier performance as well as the fiber performance, i.e., different fiber types may have different performances in different bands or sub-bands. For example, L-band may have better performance than C-band for ultra-express in most fibers. Thus, L-band can be designated for ultra-express, C-band for express, and any of the remaining bands for local. Of course, sub-band combinations are also contemplated.

The Spectral Efficiency*Reach product is an example metric that can be used to base segmentation of the bands or sub-bands. Other metrics are also contemplated such as Capacity*Distance (i.e., C*Z). Of note, there is indeed strong historical precedent for this C*Z metric, and it is frequently used in older papers which presented results far below Shannon limit and with fixed total spectral bandwidth (i.e., C-band only). Older usage (below Shannon limit, fixed spectral bandwidth) is quite useful, since results were primarily limited by trade-off between receiver bandwidth versus noise accumulation, i.e., twice Capacity˜2×noise*½ distance; C˜1/Z, where C stands for capacity and Z stands for distance. Hence C*Z could be assumed approximately constant under a fixed system design, allowing for a convenient comparison of system designs.

However, as optically amplified fiber-optic systems approach Shannon limit, the relationship changes to Capacity˜log(Es/No) when Es/No>>1. With the same assumption of approximately linear noise accumulation over distance, we get Capacity˜log(A/Z)=log(A)−log(Z), where A is constant. So, C+log(Z)˜constant. Thus, it takes very large decrease in channel distance to make a small increase in capacity possible.

For the metric, an equivalent way of looking at it is that Spectral Efficiency (SE) is purely dictated by SNR as guided by Shannon SE=2*log₂(1+SNR) for a two orthogonal polarization waveguide. Distance is being used, and has traditionally been used, as a proxy for noise accumulation (both linear and non-linear) which may not be strictly true in the case of systems with different fiber types and systems with different span lengths but is a good estimate.

Optical fiber types are generally classified based on their dispersion operation and referred to as non-dispersion shifted fiber (NDSF), dispersion shifted fiber (DSF), and non-zero dispersion shifted fiber (NZDSF). Of note, there are various types of NZDSF based on the zero dispersion wavelengths. An example of NDSF is SMF-28. Non-limiting examples of NZDSF include Truewave and variants thereof, LEAF and variants thereof, and the like. Again, the Spectral Efficiency*Reach product if a function of the fiber type and the amplifier performance.

As described herein, the terms bands and sub-bands can be used interchangeably to represent some portion of the optical spectrum. That is, a band does not necessarily mean the C-band, the L-band, etc., but could be some arbitrary portion thereof as well as crossing over these bands. The terms bands and sub-bands are just meant to denote some portion of the optical spectrum. Also, as described herein, segmentation can be on a per band or sub-band basis but can also be within a band or sub-band, as well as extend across a band or sub-band. All such embodiments are contemplated herewith.

Although the present disclosure has been illustrated and described herein with reference to exemplary embodiments providing various advantages, it will be readily apparent to those of ordinary skill in the art that other embodiments may perform similar functions, achieve like results, and/or provide other advantages. Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the spirit and scope of the present disclosure. All equivalent or alternative embodiments that fall within the spirit and scope of the present disclosure are contemplated thereby and are intended to be covered by the following claims. 

What is claimed is:
 1. A method comprising steps of: for operation on an optical fiber in an optical network with the optical fiber having an extended optical spectrum that includes a plurality of bands including at least the C-band and one or more additional bands, segmenting the plurality of bands by distance based on a metric representative of different transmission specifications for the plurality of bands, wherein the metric and the different transmission specifications are each based on fiber types and amplifiers used for corresponding bands; and placing one or more channels on the optical fiber in a corresponding band of the plurality of bands based on a distance between nodes associated with each of the one or more channels.
 2. The method of claim 1, wherein the plurality of bands include two bands and the segmenting includes a local band and an express band, the local band configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, the express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween.
 3. The method of claim 1, wherein the plurality of bands include three bands and the segmenting includes a local band, an express band, and an ultra-express band, the local band configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, the express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween, and the ultra-express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween than the express band.
 4. The method of claim 1, wherein the one or more additional bands includes a combination of sub-bands covering less than the L-band having a range of wavelengths from about 1565 nm to about 1625 nm and/or less than the S-band having a range of wavelengths from about 1460 nm to about 1530 nm.
 5. The method of claim 1, wherein the segmenting is via a tunable edge filter.
 6. The method of claim 1, further comprising performing gain flattening filtering with different specifications in different bands.
 7. The method of claim 6, wherein the C-band is used for a local band, and the one or more additional bands include an express band where the gain flattening filtering is performed with a dynamic gain equalizer (DGE) element.
 8. The method of claim 1, further comprising performing Raman amplification in select bands of the plurality of bands.
 9. The method of claim 1, further comprising utilizing a fixed multiplexer and demultiplexer structure for an express band; and utilizing a wavelength selective switch for a local band.
 10. An optical node comprising: a tunable edge filter connected to an optical fiber in an optical network, wherein the tunable edge filter is configured to segment an extended optical spectrum on the optical fiber into a plurality of bands including at least the C-band and one or more additional bands, wherein the plurality of bands are segmented by distance based on a metric representative of different transmission specifications for the plurality of bands, wherein the metric and the different transmission specifications are each due to fiber types and amplifiers used for corresponding bands, and wherein one or more channels are placed on the optical fiber in a corresponding band of the plurality of bands based on a distance associated with each of the one or more channels.
 11. The optical node of claim 10, wherein the plurality of bands include two bands and the plurality of bands include a local band and an express band, the local band configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, the express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween.
 12. The optical node of claim 10, wherein the plurality of bands include three bands and the plurality of bands include a local band, an express band, and an ultra-express band, the local band configured for transmission of optical signals between nodes having a relatively shorter distance therebetween, the express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween, and the ultra-express band configured for transmission of optical signals between nodes having a relatively longer distance therebetween than the express band.
 13. The optical node of claim 10, wherein the one or more additional bands includes a combination of sub-bands covering less than the L-band having a range of wavelengths from about 1565 nm to about 1625 nm and/or less than the S-band having a range of wavelengths from about 1460 nm to about 1530 nm.
 14. The optical node of claim 10, further comprising a plurality of gain flattening filters for the plurality of bancs with different specifications in different bands.
 15. The optical node of claim 14, wherein the C-band is used for a local band, and the one or more additional bands include an express band where the gain flattening filtering is performed with a dynamic gain equalizer (DGE) element.
 16. The optical node of claim 10, further comprising a Raman amplifier in bands with longer distances than a local band.
 17. The optical node of claim 10, further comprising a fixed multiplexer and demultiplexer structure for an express band; and a wavelength selective switch for a local band.
 18. An optical network comprising: at least two nodes with optical fibers interconnecting any of the at least two nodes; and one or more amplifier nodes between any of the at least two nodes, each of the at least two nodes include a tunable edge filter connected to the optical fibers, wherein the tunable edge filter is configured to segment an extended optical spectrum on the optical fibers into a plurality of bands including at least the C-band and one or more additional bands, wherein the plurality of bands are segmented by distance based on a metric representative of different transmission specifications for the plurality of bands, wherein the metric and the different transmission specifications are each due to fiber types and amplifiers used for corresponding bands, and wherein one or more channels are placed on the optical fibers in a corresponding band of the plurality of bands based on a distance associated with each of the one or more channels. 